This invention relates to a motherboard for a computer of the AT type, comprising a connector for a fiber card to be arranged vertically on the plane of the motherboard and a riser card arranged in that connector, said riser card having a predetermined number of positions for expansion cards and comprising a number of connectors, substantially arranged in a row parallel above each other, for such expansion cards, while the plane of an expansion card, when it is arranged in a connector of the fiber card, extends substantially parallel to the plane of the motherboard.
A (personal) computer of the AT type or a computer which is compatible therewith always comprises a motherboard on which are provided the processor, memory chips, various integrated circuits, for instance for the BIOS, video functions, etc., and connectors for the linking cables of, for instance, an internal hard disk, an internal floppy disk drive of an internal CD-ROM player, etc. Often it is desirable that such a motherboard can be extended with so-called expansion cards already during manufacture or possibly later by the user. Such cards can for instance be video cards, audio cards, control cards for an external CD-ROM player, telefax cards, modem cards, etc. Existing expansion cards are mostly of the so called ISA type and consist of a printed circuit board with electronic components thereon, a number of contact strips provided on the side of the card, which are intended to be placed in a connector of the ISA type arranged on the riser card, and a plate-shaped mounting bracket mounted at one end of the often elongated card and extending perpendicularly to the plane of the card, by means of which the card can be mechanically connected to the housing of the computer, for instance by means of a screw, and on which any terminals for equipment to be externally connected to the card can be provided.
Initially, motherboards for personal computers of the AT type were designed in accordance with the so-called AT form factor, whereby the motherboard itself was provided with a number of connectors for receiving the contact strips on the side of the expansion card. Then the expansion cards extend perpendicularly to the plane of the motherboard.
A drawback of such motherboards was that due to the height of the expansion cards, the case for the computer had to be rather high, which was often undesirable, and that the cooling of the electronic components on the expansion cards was far from optimal due to the vertical arrangement thereof.
Accordingly, for a few years now, for motherboards, use has been made of the so-called LPX form factor (LPX=Low Profile Extender). The motherboard then comprises a connector for a plug-on or so-called riser card. This is a printed board with printed circuitry on which, in a row parallel above each other, a number of connectors are arranged. On one side the riser card comprises contact strips by which it is placed in a connector arranged centrally on the motherboard, in such a manner that the fiber card sits at right angles to the plane of the motherboard. When an expansion card is arranged in the connectors of the riser card, the expansion card comes to lie parallel to the plane of the motherboard. Advantages of motherboards built up in accordance with the LPX form factor are that expansion cards can be fitted or removed from the side of the case; that the cooling of the components on the expansion cards, which are now directed horizontally, is better; and that three to five expansion cards can be arranged without having to arrange as many connectors on the motherboard, as in the case of the AT form factor motherboards, which enables the use of smaller motherboards.
For some time now, in personal computers of the AT type, in addition to the standardized AT bus signals, use has also been made of so-called PCI (Peripheral Connect Interface) signals, which must also be transmitted to and from expansion cards of the PCI type. Such PCI expansion cards have a different configuration of contact strips on the printed circuit board and consequently fit only in a specific PCI connector, which differs from the connectors for the conventional ISA expansion cards.
To make it possible to arrange both ISA expansion cards and PCI expansion cards on a riser card, it has previously been proposed to provide, at one position of the riser card, a connector intended for an ISA expansion card as well as a connector intended for a PCI expansion card, above each other. The result is a so-called combi-connector, consisting of two connectors, so that at one position, as desired, an ISA expansion card or a PCI expansion card can be arranged. However, the drawback of this solution is that due to the physical design and dimensions of the PCI expansion cards, of the ISA expansion cards and of the Connectors therefor, it is necessary to arrange the PCI expansion cards on the upper part of the riser card, i.e. farthest removed from the motherboard, and the ISA expansion cards on the lower part of the riser card. As a result, the linking tracks to the PCI expansion cards, which process high frequency signals (33 MHz), are longest, which is undesirable. Further, the PCI expansion cards, on which the components, with respect to an ISA expansion card, are arranged on the other side of the card, come to lie in the connector on the riser card in such a manner that the components are directed downwards, i.e. in the direction of the motherboard. This is undesirable for proper cooling of the components. Cooling is already problematic as it is, because the riser card arranged centrally of the motherboard highly impedes the air flow along the expansion cards.
It is noted that WO-A-93/20517 discloses a riser card on which in a line next to each other an ISA connector and a PCI connector are provided. However, the card involved here is a special type of riser card, which comprises supplementary logic circuits which are intended to convert the specific logic of the expansion card, such as ISA, PCI, Local Bus, RISA, MCA, etc., into logic which is suitable for a "processor-direct bus" on the motherboard.
It is noted that U.S. Pat. No. 5,121,295 discloses a computer with a motherboard comprising on the side thereof a connector for a riser card. However, this concerns a notebook computer and not a desktop computer as with the present invention, and the riser card only comprises a single connector for an expansion card.